An acute hypersensitivity reaction due to exposure to a previously encountered ANTIGEN. The reaction may include rapidly progressing URTICARIA, respiratory distress, vascular collapse, systemic SHOCK, and death.

Synonyms: Anaphylactoid Reaction, Anaphylactoid Shock, Anaphylaxis, Anaphylactoid Reactions, Reaction, Anaphylactoid, Anaphylactic Shock, Reaction, Anaphylactic, Shock, Anaphylactoid, Shock, Anaphylactic, Anaphylactic Reaction, Anaphylactic Reactions